Advanced Micro Devices is one of the leading manufacturers of CPUs and GPUs. It is the leading rival of not only Nvidia but of Intel. The company has provided many outstanding cards in the silicon market and has now established its dominion. One of the first things which the company introduced was its support for the Resizable BAR (AKA Smart Access Memory) feature on the new Ryzen 5000 desktop CPUs and RX 6000 GPUs. But now, the company has announced that it might never offer backward compatibility with its older Zen models like Ryzen 3000, 2000, and 1000.
According to sources, the Resizable BAR feature is actually part of the PCIe gen 3 specs and is supported by all motherboards and CPUs that are compatible with the PCIe 3.x features. But AMD has other plans for its Zen-based CPUs. But AMD’s rival Intel’s CPUs all the way back to 2014 are eligible for a Resizable BAR BIOS update.
Zen2 CPUs use the same IO die and PCIe controller as Zen3, but AMD SAM in Zen3 models are actually controlled through a new ISA CPU instruction set. The instructions are only emulated in microcode using other similar instructions in the Zen2 and older cores. Thus everything predating the new Ryzen 5000 becomes too slow to benefit from the performance uplift offered by AMD SAM.
AMD’s Frank Azor stated regarding the AMD SAM compatibility with previous CPUs that “look into it and see if it is going to be possible to do it with any performance uplift and any reliability, and please stay tuned.” It is interesting that the company is offering its AMD SAM feature at this stage of the company. It makes one expect that the company will surely offer some more features in the coming future.